Orthogonal frequency division multiplexing (OFDM) is a type of multi-carrier modulation technology, and an existing communications system such as long term evolution (LTE) or worldwide interoperability for microwave access (WIMAX) all use the OFDM technology. M serial signals (where M is a natural number) are input at a transmitter end of the communications system, serial-to-parallel conversion is performed on the M serial signals to output M parallel signals, M parallel signals carried by M subcarriers are output after the M parallel signals are modulated by M submodulators, and the M parallel signals carried by the M subcarriers are configured with a same frequency domain resource, respectively, and are transmitted through M channels. FIG. 1A is a schematic diagram of a subcarrier in a frequency domain in the prior art, where the subcarrier is presented as a sinc spectrum in the frequency domain, a frequency domain bandwidth of the subcarrier is 2Δf, an interval is Δf, and a corresponding time domain resource T=1/Δf. As can be seen from the above, the subcarrier in the prior art has a fixed frequency domain resource and a fixed time domain resource.
In an existing communications system, a transmitter end allocates frequency domain resources of a same size to subcarriers according to pre-configuration of the system. FIG. 1B is a schematic diagram of a group of subcarriers in the frequency domain, where five subcarriers are shown. As the system configures the same frequency domain resource for each subcarrier, a fixed frequency bandwidth interval exists between two adjacent subcarriers. As shown in FIG. 1B, the fixed frequency bandwidth interval is Δf.
During the process of studying the prior art, the inventor finds that, as responses of channels for transmitting subcarriers are different, frequency shifts to different extents may occur on the subcarriers in the transmission process, and amplitudes of the subcarriers may also be attenuated to different extents. When a frequency interval of a fixed size is configured between subcarriers, and particularly when the frequency interval of the fixed size is relatively small, a frequency bandwidth interval between two adjacent subcarriers is also relatively small. Therefore, in the transmission process, the subcarriers may overlap due to frequency shifts, making the system lose orthogonality, and it is difficult for the system to achieve maximum spectrum efficiency, affecting performance of the communications system.